Fluid steering system for vehicles



G. J. BAUDHUIN El AL FLUID STEERING SYSTEM FOR VEHICLES Original FiledNov. 1 1959 5 Sheets-Sheet 1 G. J. BAUDHUIN ETAL Re. 25,

FLUID STEERING SYSTEM FOR VEHICLES 3 Sheets-Sheet 2 Original Filed Nov.16, 1959 Nov. 6, 1962 G. J. BAUDHUIN ErAL 25,280

FLUID STEERING SYSTEM FOR VEHICLES Original Filed Nov. 16, 1959 5Sheets-Sheet 3 United States Pant thee Re. 25,230 Reissued Nov. 6, 196225,280 FLUID STEERING SYSTEM FOR VEHI CLES George J. Baudhuin and ArnoldC. Petersen, Sturgeon Bay, Wis., assignors, by mesne assignments, toDrott Manufacturing Corporation, Milwaukee, Wis., a corporation ofWisconsin Original No. 3,028,925, dated Apr. 10, 1962, Ser. No.

853,109, Nov. 16, 1959. Application for reissue May 23, 1962, Ser. No.197,207

11 Claims. (Cl. ISO-79.2)

Matter enclosed in heavy brackets appears in the original patent butforms no part of this reissue speciiication; matter printed in italicsindicates the additions made by reissue.

This invention relates to an hydraulic steering system forself-propelled vehicles.

In certain vehicles, such as in a gantry type mobile lift device, thespacing between the wheels must remain open and unencumbered. It is animportant object of this invention to provide an improved system forturning the wheels of such a vehicle in controlled relation to eachother, which system does not employ any mechanical linkages tointerconnect the spaced wheels,

Another object of this invention is to provide a system for turning thewheels of a vehicle, which system will effect turning of the wheel atthe inside during a turn through a relatively greater angle than thewheel at the outside, to thereby accommodate the different turningcenters of the wheel.

A more particular object of this invention is to provide a steeringsystem including a pair of steering cylinders connected to respectiveones of the wheels on the vehicle to effect steering of the same, a flowreversing valve for reversibly controlling the flows of fluid to andfrom the several cylinders, and an arrangement for hydraulicallyinterconnecting the cylinders with each other to equalize movement ofthe pistons therein.

Yet another object of this invention is to provide a steering system inaccordance with the foregoing object in which the position of theoperator of the flow reversing valve is always correlative with theangular position of the steering wheels to facilitate maneuvering thevehicle.

These, together with various ancillary objects and advantages of thisinvention will be more readily appreciated as the same becomes betterunderstood by reference to the following detailed description when takenin connection with the accompanying drawings wherein:

FIGURE 1 is a side elevational view of a mobile lift device embodyingthe invention of the present application;

FIG. 2 is a front elevational view of the mobile lift device;

FIG. 3 is a fragmentary horizontal sectional view taken on the plane 33of FIG. 1 and showing the front steering wheels in the straight aheadposition;

FIG. 4 is a fragmentary horizontal sectional view through the frontgantry frame and showing the vehicle wheels turned to one limitingposition thereof;

FIG. 5 is a schematic diagram illustrating the hydraulic steeringsystem; and

FIG. 6 is a fragmentary vertical sectional view taken on the plane 66and illustrating the manner of mounting the control valve for turningmovement with the steering wheel forks.

The present invention relates to improvements in bydraulic steeringsystems in which the relative turning of the separate steering wheels iscontrolled hydraulically instead of mechanically. Since the steeringsystem of the present invention does not employ any mechanical linkagesto interconnect the separate steering wheels, it is particularly adaptedfor use in connection with vehicles, such as the gantry type mobile liftdevice shown in the patent to George I. Baudhuin No. 2,909,298, whereinit is necessary to maintain the space between the wheels open andunencumbered. In the present application, the hydraulic steering systemis described as applied to such a gantry type mobile lift.

As more specifically described in the aforementioned patent, the mobilelift includes a pair of generally U- shaped gantry frames 10 and 11which are interconnected at their lower ends by spaced side members 12.The frames each include upright side members 13 and a connecting bridgeportion 14 which extends between the upright side members. In thespecific form shown, the frame 10 is rigidly secured to the side members12 and the frame 11 is adjustably secured thereto as by sleeves 16 whichare slidable along the side members and selectively locked in adjustedposition by screws 17. A set of rear wheel forks 18 are mounted on thesleeve 16 and have rear support wheels 19 journaled therein. Front wheelforks 21 are mounted for turning movement about an upright axis 22 atthe lower ends of the legs 13 of the frame 10 and front wheels 24 arerotatably journaled in the front wheel forks. The steering wheels ateach side of the vehicle and the apparatus for turning the same aresimilar and, for convenience, like numerals together with the letters Land R are utilized to designate corresponding parts on the left andright sides of the vehicle, respectively.

The steering wheels 24 are preferably also the drive wheels and, asshown, an hydraulic motor and gear reducer unit 31 is mounted as by abracket 32 on each of the forks 21, for turning movement therewith. Themotor and gear reducer unit 31 is connected through a chain 33 to asprocket 34 on the respective one of the Wheels 24 to reversibly drivethe same. Fluid under pressure is reversibly supplied to the drive units31 from a pump assembly 37 driven by an engine 38. The pump assembly 37draws fluid from a reservoir 39 and delivers the same to a 4-way valveassembly 41 which reversibly con trols the flow of fluid to the drivemotors 31, all in a manner specifically described in the aforementionedpatent. The valve asembly 41 also includes 4-way valves for reversiblycontrolling the flows of fluid to the hydraulic winch motors 42 whichoperate to elevate and lower the tackle blocks 43. The specific vehicledrive system forms no part of the present invention and further detaileddescription thereof is deemed unnecessary.

The hydraulic steering system of the present invention includes asteering unit 45 for each of the steered wheels 24 and a 4-way flowreversing valve 46 for reversibly controlling the flows of fiuid to apair of the steering units. In the form illustrated, only the frontwheels of the vehicle turn, and a single pair of steering units areprovided. These steering units each include a cylinder 47 and a piston48 which is slidable in the cylinder and has a rod 49 extending out ofone end thereof. The steering units are connected to the respectivesteering forks and to the side members 12 of the vehicle, and, in thespecific form shown, the cylinders 47 are pivotally mounted by an arm 51and bracket 52 for horizontal swinging movement on the side members 12of the vehicle frame. The rods 49 of the steering units are pivotallyconnected by a pin 53 to an car 54 on the respective steering wheelbracket or fork 21. The steering units are arranged so as to turn thefork at the inside during a turn through a relatively greater angle thanthe fork at the outside of the turn, to accommodate the differentturning radii of the wheel due to the lateral spacing therebetween. Thisis achieved in the present device by locating the pivot pins 53, whichconnect the steering units to the forks, at the outboard side of theturning axes of the respective steering forks and at a point such thatthe line through the pivot pin 53 and the turning axis 22 defines anangle of greater than ninety degrees, when the wheels are positioned forstraight ahead movement as shown in FIG. 3. With this arrangement, theforks 21 will be turned through a greater angle when the piston isretracted than when the piston is extended a corresponding distance. Asshown in FIG. 4. the left fork 21L is turned through an angle ofapproximately thirty-two degrees when the piston of the left steeringunit 45L is retracted a preselected amount, and the right steering fork21R is turned in the same general direction, and through a lesser angleof approximately twenty-five degrees, when the piston of the rightsteering unit 45R is extended a corresponding distance. Angularly spacedstops 61 and 62 are provided on each of the forks 21, and cooperate witha stationary stop member 63 mounted on the lower ends of the forwardframe 10, to limit the angular movement of the forks. The angularposition of the stops 61 and 62 is correlated with the differentialturning rate of the steering wheels, the stops 62 being arranged tolimit movement of the forks as the respective pistons are retracted andthe stops 61 being arranged to limit angular movement of the forks whenthe respecitve pistons are extended. Necessarily, the differential rateat which the forks are turned will vary dependent on the width of thevehicle and the difference in the turning radii of the wheels.

Fluid under pressure is supplied to the steering units 45 by means of apump 37a and the flow reversing valve 46. The pump 37a is one of thepumps in the assembly 37 which is driven by the engine 38 and has itsinlet 66 connected to the reservoir 39. The flow reversing valve has afluid inlet 67 connected to the outlet of the pump through a conduit 68,and a return outlet 69 which is connected to the reservoir through aconduit 71. The flow reversing valve also has a pair of controlledoutlet ports 72 and 73 which are connected through conduits 74 and 75 tothe left and right steering cylinders 45L and 45R respectively. Thevalve has a valve bore 78 therein and a spool valve member 79 which isslidable in the bore. The pressure inlet port 67 communicates throughlateral passages 81 and 8121 with the valve bore intermediate the endsthereof, and the return passage 71 communicates through passage 82 withthe bore adjacent opposite ends. The controlled outlet or work ports 72and 73 communicate through ports 84 and 85 with the valve bore. When thevalve is in its neutral position shown in FIG. 5, the spool member 79blocks the work ports 84 and 85 and communicates the pressure inlet port81 through a return port 82b with return passage 82 to thereby bypassthe pump discharge back to the reservoir. When the spool member 79 ismoved in one direction from its neutral position, such as to the left asviewed in FIG. 5, fluid under pressure will be supplied from the inletpassage 81 to the work port 84 for flow through the conduit 74 to theright hand steering cylinder 45R and, simultaneously, the left handsteering cylinder will be communicated through conduit 75, work port 85,and return passage 82 to the return line 71. The pistons in the left andright steering cylinders will therefore be moved in relatively oppositedirections to extend the right hand cylinder and retract the left handcylinder and thereby turn the wheels to the left. Conversely, when thespool 79 is moved to the right as viewed in FIG. 5, fluid pressure willbe supplied to the cylinders in a direction to turn the wheel to theright. A pressure relief valve 88 is preferably provided between theinlet and return passages 67 and 82 to prevent overloading of the pump,and cross relief valves 89 and 91 located in a casing 90 are providedbetween the work conduits 74 and 75 to prevent overloading of the systemor stressing of the parts in the event one wheel strikes an obstructionwhich prevents it from turning.

In order to prevent turning of the steering wheels at relativelydifferent rates, provision is made for hydraulically interconnecting thecylinders 45L and 45R. For this purpose, a connecting conduit 92 isprovided and communicates with the respective cylinders at the side ofthe piston 48 therein opposite the side with which the conduits 74 and75 communicate. This forms a closed hydraulic circuit between thecylinders at one side of the piston therein so that fluid displaced fromone cylinder as one piston is extended, is passed to the other cylinderand moves the piston therein to its retracted position to thereby effectequal but opposite movement of the pistons in the left and rightsteering cylinders.

Since the relative movement of the cylinders is controlled by the closedhydraulic circuit including the connecting conduit 92, it is apparentthat any leakage from the closed circuit will preclude the vehiclewheels from tracking properly. Such leakage may occur around the pistons48 in the cylinder and, in order to compensate for such leakage, abypass conduit 95 is provided and is connected between the connectingconduit 92 and one of the work conduits such as 74. A manually operablebypass valve 96 is provided in the bypass conduit and is adapted, whenopened, to pass fluid from the work conduit 74 to the connecting conduit92. In order to readjust the cylinders so as to effect proper turning ofthe respective forks, the control valve is operated to a position tosupply pressure to the conduit 74 until the steering fork 21R reachesits limiting position in which the stop -61 abuts against the stopmember 63. If fluid has leaked from the closed circuit including theconnecting conduit 92, the left hand fork will not yet have reached itslimiting position in which the stop 62 engages the stop member 63. Theby-pass valve 96 is then opened and continues to supply fluid to theconnecting conduit 92, which fluid operates on the piston 48 in the leftsteering cylinder and moves the left fork until the stop 62 engages thestop member 63. At that time the bypass valve 96' is shut off.

Movement of the valve spool 79 is effected by means of a manuallyoperable lever 101 which is pivotally mounted by a pin 102 on the valvebody and pivotally connected intermediate its ends by a pin 103 to thevalve spool. Steering of the vehicle is thus effected by manipulation ofthe lever 101. In order to facilitate maneuvering of the vehicle, thevalve is mounted and arranged so that the operating lever position will,at all times, be correlative with the angular position of the wheels.For this purpose, the valve body is mounted as a rod 104 and bracket 105for turning movement about an axis parallel to the turning axes 22 ofthe steering forks. The operating lever 101 is mounted by the pin 102for horizontal swinging movement relative to the valve body about anaxis which is parallel and preferably closely adjacent to the axis ofthe rod 104. The rod 104 is connected through an arm 108 and link 1539to an ear 110 on the right steering fork 21R so that the valve body willturn in response to turning of the right fork. As shown in FIG. 3, theoperating lever 101 is arranged to extend forward, when the vehiclewheels 24 are positioned for straight ahead movement, and the valve andits operating lever will move to the left or to the right as the vehiclewheels are respectively turned to the left and to the right.

From the foregoing it is thought that the operation of the device willbe readily understood. Since the relative movement of the Wheels iscontrolled entirely hydraulically, no mechanical linkage between thewheels is required, The steering system is therefore particularlyadapted for use on those vehicles such as the gantry type mobile liftdevice shown wherein it is necessary to maintain the space between thewheels open and unencumbered. The conduit 74 leading to the leftcylinder and the connecting conduit 92 can be easily mounted at anyconvenient location and as best shown in FIG. 2, are arranged to extendupwardly along the legs of the U-shaped frames and across the bridgeportion 14 thereof. Fur

ther, although the position of the wheels is controlled hydraulically,the valve operating lever is nevertheless so arranged as to indicate, atall times, the angular position of the wheels to facilitate maneuveringof the vehicle.

We claim:

1. In combination with a vehicle having spaced steering Wheel bracketsmounted for turning movement about an upright axis and a Wheel rotatablymounted on each bracket, an hydraulic steering system providing the solemeans for controlling relative turning movement of said Wheel brackets,said hydraulic steering system comprising a pair of pressure cylinderseach having a piston slidable therein, means connecting the pressurecylinders to respective ones of the wheel brackets at points laterallyoffset from relatively opposite sides of the respective turning axis ofthe brackets to effect turning of both brackets in the same direction inresponse to extension of one piston and retraction of the other, a fluidpump, a flow reversing valve connected to the pump and having first andsecond controlled outlet ports each connected to a respective one of thecylinders at one side of the pistons therein to effect movement of thepistons in relatively opposite directions, means mounting said valve forturning movement about an axis parallel to the turning axis of saidWheel brackets, means operatively connecting said valve to one of saidwheel brackets to effect turning of said valve in a direction andamplitude correlative with the turning of the Wheel bracket, said valvehaving an operating lever movable relative to the valve about an axisparallel to the turning axis of the valve whereby the angular positionof the lever is correlative with the angular position of the wheelbrackets, and a fluid conduit connected to said cylinders at the othersides of the pistons therein to intercornmunicate the cylinders witheach other and pass fluid from one cylinder to the other as the pistonsin the cylinders move in opposite directions to equalize the movement ofthe pistons in opposite directions.

2. The combination of claim 1 wherein said connecting means includes alinkage.

3. In combination with a gantry-type mobile lift having spaced legs anda connecting bridge portion, a steering wheel bracket mounted on eachleg for turning movement about an upright axis, a wheel rotatablymounted on each bracket, an hydraulic steering system providing the solemeans for controlling relative turning movement of said wheel brackets,said hydraulic system comprising a pair of pressure cylinders eachhaving a piston slidable therein, means connecting the pressurecylinders to the Wheel brackets to effect turning of the latter inresponse to extension and retraction of the cylinders, a fluid pump, aflow reversing valve located adjacent one leg of the mobile lift andconnected to said pump and having first and second controlled outletports, a first conduit ex tending from said first controlled outlet portto the steering cylinder on said one leg of the mobile lift, a secondconduit extending from said second controlled outlet port and along saidbridge portion to the steering cylinder on the other leg of the mobilelift, said first and second conduits each communicating With therespective cylinders at one side of the piston therein, a connectingconduit communicating with each of said cylinders at the other sides ofthe pistons therein and extending alongside the legs and connectingbridge portion of the lift to effect turning of the wheels in controlledrelation to each other, said valve including a valve body mounted forturning movement about an axis parallel to the turning axis of saidwheel brackets, a valve operating lever mounted for movement relative tothe valve about an axis parallel to the turning axis of the valve, andmeans connecting said valve body to the adjacent steering wheel bracketfor turning the valve body in a direction and amplitude correlative withthe direction and amplitude of turning movement of the wheel bracket.

4. In combination with a gantry-type vehicle having an upright U-shapedframe, spaced wheel forks mounted on the frame for turning movementabout an upright axis and a wheel journaled on each fork, an hydraulicsteering system providing the sole means for controlling relativeturning movement of said wheel forks, said hydraulic system comprising apair of steering units each including a cylinder and piston slidable inthe cylinder, means pivotally attaching opposite ends of the steeringunits to the frame and to the steering forks, the pivotal connection ofthe units to the forks being laterally offset from the turning axis ofthe forks and located at the outboard side of the vehicle at a point toeffect turning of the Wheel bracket at the inside during a turn througha relatively greater angle than the wheel at the outside during a turnin response to extension of one operator and retraction of the otheroperator substantially equal distances from a neutral position, areservoir, a pump for pumping fluid from the reservoir, a flow reversingvalve having first and second controlled outlets, first and secondconduits connected to said first and second outlets and to a respectiveone of said cylinders at one side of the piston therein, to effectsimultaneous movement of the pistons in relatively opposite directions,a connecting conduit communicating with said cylinders at the othersides of the pistons therein for passing fluid from one cylinder to theother and thereby equalize the movement of the pistons in oppositedirections, means mounting said valve for turning movement about an axisparallel to the turning axis of one wheel fork, said valve having anoperator movable relative thereto about an axis parallel to the turningaxis of the valve, and means connecting the Valve to one wheel fork toturn the valve in a direction and amplitude correlative with thedirection and amplitude of turning of the forks whereby the operatinglever for the valve is correlative with the position of the Wheel forks.

5. In combination with a vehicle having a frame, first and second spacedsteering wheel brackets mounted on the frame for turning movement aboutan upright axis, and a Wheel rotatably mounted on each bracket; anhydraulic steering system providing the sole means for controllingrelative turning movement of said wheel brackets, said steering systemcomprising first and second steering units each including a cylinder anda piston slidable in said cylinder, means pivotally attaching oppositeends of the first and second steering units to the frame and to thefirst and second steering forks respectively at points laterally offsetfrom relatively opposite sides of the respective turning axis to effectturning of both brackets in the same direction in response to extensionof one piston and retraction of the other piston, said first and secondsteering units being arranged relative to the respective steering forksto efiect turning of the wheel at the inside during a turn through arelatively greater angle than the Wheel at the outside during a turn inresponse to extension of one piston and retraction of the other pistonsubstantially equal distances from a neutral position in which the Wheelforks are positioned for straight ahead movement, a reservoir, a pumpfor pumping fluid from the reservoir, a flow reversing valve havingfirst and second controlled outlet ports each connected to a respectiveone of the cylinders at one side of the piston therein to effectmovement of the pistons in relatively opposite directions, a fluidconduit connected to said cylinders of said first and second units atthe other sides of the pistons therein to communicate said cylinderswith each other and pass fluid from one cylinder to the other as thepistons in the first and second steering units move in oppositedirections, first and second stop means engageable With said first andsecond wheel brackets to limit turning in at least one direction, thepositions of said first and second stop means being correlated With thedifferential turning movement produced by said steering units to limitmaximum turning of the wheel bracket at the inside during a turn to arelatively greater angle from straight ahead positionthan the wheelbracket at the outside during the turn, a by-pass conduit having one endconnected to said fluid conduit and the other end connected to receivefluid under pressure from said pump, and a bypass valve in said bypassconduit adapted to be opened when one wheel bracket is against its stopmeans to supply fluid under pressure to said fluid conduit and replenishany loss of fluid from said cylinders at said other side of the pistonstherein whereby to move the other wheel bracket against its stop meansto re-align the wheels.

6. In combination with a gantry-type mobile lift including a framehaving spaced legs and a connecting bridge portion, first and secondsteering wheel brackets mounted on the legs of for turning movementabout an upright axis and a wheel rotatably mounted on each bracket; anhydraulic steering system providing the sole means for controllingrelative turning movement of said wheel brackets, said hydraulic systemcomprising first and second steering units each including a cylinder anda piston slidable in said cylinder, means pivotally attaching oppositeends of the first and second steering units to the frame and to thefirst and second steering forks respectively at points laterally offsetfrom relatively opposite sides of the respective turning axis to efiectturning of both brackets in the same direction in response to extensionof one piston and retraction of the other, said first and secondsteering units being arranged relative to the respective steering forksto efiiect turning of the wheel at the inside during a turn through arelatively greater angle than the wheel at the outside during the turnin response to extension of the piston in one unit and retraction of thepiston in the other unit substantially equal distances from a neutralposition, in which the wheel forks are positioned for straight aheadmovement, a reservoir, a pump for pumping fluid from the reservoir, aflow reversing valve located adjacent one leg of said mobile lift andconnected to the pump and having first and second controlled outletports, a first conduit extending from said first controlled outlet portto the cylinder of said first steering unit on said one leg of themobile lift, a second conduit extending from said second controlledoutlet port and along said bridge portion to the cylinder of said secondsteering unit on the other leg of the mobile lift, said first and secondconduits communicating with the cylinders of said first and secondsteering units at one side of the pistons therein, a connecting conduitcommunicating with each of said cylinders at the other sides of thepistons therein and extending alongside the legs and connecting bridgeportion of the lift to effect turning of the Wheels in controlledrelation to each other, first and second stop means engageable with saidfirst and second wheel brackets to limit turning in at least onedirection, the positions of said first and second stop means beingcorrelated with the differential turning movement produced by saidsteering units to limit maximum turning of the wheel at the insideduring a turn to a relatively greater angle from straight ahead positionthan the wheel bracket at the outside during the turn, a by-pass conduithaving one end connected to said connecting conduit and the other endconnected to receive fluid under pressure from the pump, and a by-passvalve in said by-pass conduit adapted to be opened when one wheelbracket engages its stop means to supply fluid under pressure to saidcylinders at said other side of the pistons therein whereby to move theother wheel bracket against the repective stop means to re-align thewheels.

7. A steering system comprising, a horizontally disposed frame, a wheelfork pivotally mounted to said frame about a first generally verticalaxis, a hydraulic motor connected to said frame and to said fork, afluid pressure source, a valve between said source and said hydraulicmotor for controlling the supply of fluid to said motor for actuatingthe same to cause said fork to pivot with respect to said frame, meansmounting said valve for turning movement about a second axis parallel tosaid first axis, a teering lever movable relative to said valve about anaxis parallel to said second axis and connected to said valve forcontrolling the expansion and contraction of said motor in response tomovements of said lever, and a linkage connecting said valve to saidfork to efiect a movement of said valve about said second axis in adirection and amount corresponding to the movement of said fork.

8. A steering system comprising, a horizontally disposed frame, a wheelfork pivotally mounted to said frame about a first generally verticalaxis normal to said frame, a horizontally disposed steering leverpivotally mounted about a second axis parallel to said first axis, meanscausing said wheel fork to turn in an amount and direction correspondingto an amount and direction of movement of said lever, said meanscomprising, a fluid pressure source, a hydraulic motor between saidframe and said fork, a valve between said source and said motor, saidvalve comprised of a valve housing movable angularly with said wheelfork, and a movable member connected to and movable with said lever,said movable memher having a first position causing said motor to turnthe fork in one direction, a second position causing said motor to turnthe fork in the other direction, and a third neutral position betweensaid first and second positions, whereby when said steering lever ispivoted in a first direction, said movable member moves from saidneutral position to said first position, causing said wheel fork topivot in said first direction and said housing to move with respect tosaid movable member, and thereby returning said movable member to saidneutral position.

9. A hydraulic steering system for turning a pair of laterally spacedvehicle wheels in controlled relation to each other and for causing saidwheels to follow the angular movements of a horizontally disposedsteering lever, comprising, a frame, a pair of wheel supporting forkspivotally mounted to said frame, a pair of pressure steering cylinderseach having a piston slidable therein, means connecting each cylinder toone of said wheel forks for turning the latter in response to extensionand retraction of the piston, a source of pressurized fluid, a fluidcontrol valve between said cylinders and said source, said valvecomprised of a valve housing connected to and movable with one of saidwheel forks and a movable member connected to and movable with saidcontrol lever, said movable member having a first position causing oneof said cylinders to extend and the other to contract, a second positioncausing said one cylinder to contract and said other cylinder to extend,and a third neutral position between said first and second positions,whereby when said lever is pivoted in one direction, said movable membermoves from said neutral position to said first position and causes saidwheel forks to pivot in said one direction and said housing to move withrespect to said movable member, and thereby returning said movablemember to said neutral position.

10. A hydraulic steering system for turning a pair of laterally spacedvehicle wheels in controlled relation to each other and for causing saidwheels to follow the angular movements of a horizontally disposedsteering lever, comprising, a frame, a pair of wheel supporting forkspivotally mounted to said frame, a pair of pressure steering cylinderseach having a piston slidable therein, means connecting each cylinder toone of said wheel forks for turning the latter in response to extensionand retraction of the piston, a source of pressurized fluid, a fluidcontrol valve between said cylinders and said source, said valvecomprised of a valve housing connected to and movable with one of saidwheel forks and a movable member connected to and movable with saidcontrol lever, said valve housing having two ports connectedrespectively to one end of said cylinders, said movable member beingmovable to different positions to connect said ports alternately andselectively to said source or to a fluid return,

a conduit interconnecting the other ends of said cylinders, stops tolimit turning of said forks in either direction, and means including avalve to supply fluid under pressure to said conduit.

11. A steering system comprising, a horizontally disposed frame, a wheelbracket pivotaliy mounted to said frame about a first axis, a hydraulicjack having a first end mounted to said frame and a second end mountedto said bracket, a fluid pressure source, a valve between said sourceand said jack for controlling the fluid to said jack for expanding andcontracting said jack causing said bracket to pivot with respect to saidframe, means mounting said valve for turning movement about a secondaxis parallel to said first axis, stop means on said frame engageablewith said wheel bracket for limiting turning movement in at least onedirection, a linkage connecting said valve to said fork to efiect aturning 07 said valve in a direction and amount corresponding to themovement of said fork, and said valve having an operating lever movablerelative to said valve about an axis parallel to the turning axis ofsaid valve, whereby the angular position of the lever is correlativewith the angular position of said fork.

References Cited in the file of this patent or the original patentUNITED STATES PATENTS

